Heat exchanger



Aug. 16, 1949. A GE f 2,479,071

HHHHHHHHHHHH ER Aug; 16; l1949. A. G. HENsTRlDGE v 2,479,071

HEAT EXCHANGER Aug. 16, 1949.A A. G. HENsTRlDGE Y I 2,479,071

HEAT EXGHANGER v l vFiled July 15, 1944 4 sheets-sheet- 4 Trek/VEYPatented Aug. 16, 1949 UNITED STAT Es PATNT "oF Fi ce l Alec GeorgeHlsdiggland, assign- A I or vto The'Bristol Aeroplane Company Limited, fBristol, England, a. British company Application July l15, 1944, SerialNo. 545,161

A' I n Great Britain ,27, 1943 t section 1, Public Law 69s, August s,1946 Patent expires April 27, 1963 Y This invention concernsheat-exchangers in which one of the fluids is conveyed through aplurality of ducts and the secondfiuid hows along passages between saidducts. n f

' Heat-em'shangers of the type wherein the ducts and passages have innerand outer defining walls of different length have heretofore sufferedfrom the disadvantage that the ducts and/or passages have had anon-uniform width. )The term width as used' throughout thisspecification is to 'be understood as meaning the minimum distancebetween opposite walls of a yduct or passage at any point in .theheat-exchanger, said distance being measured in a plane at right anglesto said deiining walls. c

It will 'be appreciated that when the duct and/or passage-width is notuniform throughout Ytheir length in the piane at right angles to saiddeningwalls, an even distribution oi one uuid throughout the other isnot obtained. Y

It is'an object oi the present invention to provide .a heat-exchanger ofthe type hereinbefore set Iorth in which the widths oi the passagesy andiz claims. (ci. asv- 235) ducts are substantially uniform so as toprovide f an improved distribution.

According to the present' invention a heat- Y exchanger oi' the typehereinbefore set forth is characterised in that the ducts for one'.iiuid are curvilinear viewed in the direction of the iow of the otheriluidthrough the passages, the form of said curve `being such that thewidth' of said ducts andpassa'ges is substantially constant throughouttheir length in the plane at right angles to the direction ofv ow of'the second named Huid.

According to another feature of the invention the curvature of the ductsis, or is approximately', the locus of a point on a line that rollswithout sliding around a regular geometrical figure in the piane oftheligure.

According to another aspect of the present invention, a heat-exchangercomprising a chamber and partitions separate the hot and' cold Vfluidsextending inwards from the. periphery towards the middie of the chamber,ischaractcrised that the said partitions are curved substantially to ashape as above set forthr Preferably the curvature of the partitions orducts is, or is approximately, the locus of apoint in a straight linethat rolls without sliding around a base circle, ellipse or other closedcurved augure in which casey the generated curve is an involute orapproximates 'thereto'. However the curvature of the convergingduc'tsmay be the locus oi' a point on a generating circle that rollswithout sliding around a base circle, eilipse or other closed curvedligure in which V'case the generated curve is an epicycloid--or a-hypocycloid VIt is also possible however, to generate curves having thesame properties from a vstraight-sided non-re-entrant geometricalligure. In this latter case, the curve f geheratedcomprises two or morecircular arcs, which may offer advantages from the manufacturing pointof view. Instead of generating a curve inthe manner just described, asuitable curve'may be produced by the union of two or more circular arcssuch` that the complete curve approximates to the involute, epicycloidor hypocycioid form.

Y Speciiic embodiments oi the present invention as applied to aheat-exchanger in which one of the ilu'ids 'flows' longitudinallythrough a trunk whilst the other iiuid nows from the periphery of thetrunk which conveys the first fluid towards the middle vof the latterwill now be described merely by way of example with reference to Figures1 to 9 of the accompanying drawings whereof- Figure 1 is a parttransverse section of a heatexchanger in accordance with the presentinvention in which the ducts are of yinvolute shape, Figure 2 is asimilar view to Figure 1 in which the ducts are produced 'by the unionof two circular arcswhich approximate to the involute form shown inFigure l',

Figure '3 is a part transverse section of another construction ofheat-exchanger oi ,drum form which is `provided with ducts of involuteform,

vFigure 4' is a part transverse section of a heatexchanger in which thecurvature of the ducts is Y generated 'by the rolling of a straight linearound a hexagon.,

Figure 5 is a part transverse section of a heatexchanger in which thecurvature of theV ducts is generated as an n'vol'ute from an ellipse,

.Figure 6 is apart transverse section of aV heatexchanger in which theductsr are of epicycl'oidal forni,`

Figure '1 is atransverse section on the line 1-1 oi Figure showing onequarter of the preferred construction ot .heat-exchanger in accordancethepresent invention, Figiiire alsa section onthe line' 8--8 of Figure'7, figure 9 is a viewin 'the direction of arrow' A ci and on Mergerscale. f

'Whiie the invention is concerned with heat-exchangers in general, aheat-exchanger in accordance with the present inventionv is particularlysuitable for incorporation as one of the members ci a gas-turbinepowerplant for' aircraft. The

amaovi f i' a f changer so that as the exhaust gases from |tl`1e lturbines flow through the exchanger they w1ll give up part of theirheat-content to the'cold air.

thereby heating the latter before `itreafrshes thel l! combustionchambers.

In the particular application kof the invention referred to, threefactors are of especial imprtance, namely:

o) That whnst the pressure drop` `entailed;

4' cold-'air chambers I3 to the hot-air chambers I8.

It wil1 be understood from this general description of theheat-exchangers shown in Figures l to 6 that the exhaust-gases owthrough .'the'passag'es I 9 in a direction or'malito the plane of thepaper. The width of the ducts and passages will be measured (inaccordance with the definition set forth above) in the plane of thepaper )and will be the minimum distance between the bounding walls .ofthe ducts and passages in said plane.

The 4present invention aims at providing a particular arrangement ofducts and passages which will have aconstant or approximately constantwidth throughout their length in the plane of -across the cold side ofthe exchanger is of rel-fatively little importance the pressure-drop'across'- the hot side is material; the latter must there- 1'* fore bekept at a minimum. With this end in view the exhaust-gases from the.turbine should Vfollow a straight` path 4to* thedischarge nozzle;however, the air passing from the compressor to the heat-exchanger andthence to the combustion-chamber may without undue effect follow yacircuitous path, ,4

(ii) That of ensuring uniformity of distribution from the compressor andof supply to the turbine. This requires that as great a number ofoutlets be spaced around the delivery chamber of the compres-sor asispracticable, and that a similar disposition of inlets Ito the turbine beprovided,

(iii) That the cross-sectional area of the ducts (and of the passagesbetween them) be constant throughout their length inthe plane at rightangles to the direction of the passages between the ducts and that thewidth of both `ducts and passages, as hereinbefore explained, besubstantially uniform for the hot and cold sides of the exchanger. Thisensures that the transfer of heat for any given size of heat-exchangeris a maximum.

In each of the constructions shown in Figures 1 to 6 of the accompanyingdrawings the exhaustgases from the turbine pass by a straight pathlongitudinally through a trunk I I Whose peripheral or outer definingwall is indicated at I2. In this way the rst'factor mentioned above issatisfled. The cold air lromlthe compressor is delivr ered to aplurality of chambers I3 which are spaced around the wall I2 and extendalong the length of the drum-one end of each of the chambers isconnected with the `compressor and the other end is closed. The airpasses from chambers I3 into a plurality of ducts I4 which extendtowards the middle of the trunk and into chamber I5, and then into aplurality of ducts I6 which lead into chambers I8. k The latter, whichare spaced around the Wall I2 (being intercalated with chambers I3) andextend along the length of the drum, are connected to the turbine. Theprovision of a plurality of inter-calated cold and hot-air chambers I3and I8 which are spaced around the peripheral Wall I2 of theheat-exchanger ensures uniformity of distribution from the compressorand tothe turbine and thus meets factor (ii) referred to above. It isclear from the drawings that the exhaust-gases which pass 1ongitudinallythrough the trunk Il are constrained to flow through a plurality ofpassages I9 each of which is bounded by a pair of adjacent ducts. Inthis way the hot exhaust-gases are brought into intimate contact withthe air infducts I4 and I6 thereby heating the air whichpasses'from thethe paper.

In Figure 1 the ducts I4, I6 which in this construction extend from thewall I2 of trunk II to inner defining wall I'I of a central collector I5lie upon a curved path. yThe curvature of the ducts is generated bytherolling of.,a straight line around the wall ofthe central collectorI5, that is the ducts I4, I 6 are of an involute shape. Asis clearlyshown in Figure 1, with .this construction the provision of ducts ofuniform width throughout their length (as occurs when the ducts are madefrom parallel-wall tube of diameter a) will result in the passagewidth balso being constant throughout the length of ,the ,'ducts. Accordingly aheat-exchanger constructed as shown in Figure 1 will completely satisfythe three conditions stated to be essential in a heat-exchanger for agas turbine power-plant.

In the construction shown, in Figure 2 the curvature of the ducts I4,.IB is produced by the union of two circular arcs so as closely toapproximate to the involute form shown in Figure 1. The portion of theducts which lie'sl adjacent the wall I1 is a circular arc having aradius R1 whilst the portion of the ducts adjacent the wall I2 isacircular arc Whose radius is equal to R2. With this con-struction theduct width a may be made uniform by constructing' the ducts fromparallel-wall tube and although the passage width b is not absolutelyconstant throughout the length'of the ducts I4,` IIS, by'suitablyselecting the radii R1 andR2 it is possible so to arrange matters thatthe passage width will vary by only a small amount over' the rlength ofthe ducts. Any disadvantage which may accrue fromsuch non-'uniformity inthe width of the passages may be off-set from the manufacturing point ofview.

The shape of the ducts I4, I6 shown in Figure 3 being of involute formandthe ducts having a .uniform width a throughout their length itfollows that the passage width b will also be constant throughout thelength of ysaid ducts. In this construction the central collector I5 hasbeen dispensed with and the cold air flows directly from one of thecold-air chambers I3 to its associated hot-air chamber IB, along a ductwhich is substantially U-shaped. The limbs I4, I6 of each duct (whichare ofinvolute form) have their innerl extremities connected by anarcuate portion 20 so that the coldair from chamber I3 will pass downlimb I4 ofthe duct, around the portion 20 and up the other limb I5 tothe hot-air chamber I I3. It will be noted from Figure 3 thatth'e'U-shaped ducts are stacked one within the other, and that all thelimbs I4 of each stack are associated with a cold-air chamber I3 whilstthe limbs I6 of each stack are associated with the adjacent hot-airchamber I8. The inner ends accom-.1

:of the Ypassages .t9 .for the exhaust gases .are bounded loyiawall 2l.x t

kfIn 'the ,construction .shown fin..,Figure A `the v.central collectorI5 .is .hexagonal Vin .cross-section andthe .ducts I4, I6.aregeneratedriby the rolling vof :a .straight `linearound the hexagonalchamber. As .a conseouencefthe .ductsiareztormed bythe .junction iof a:number :of circular .arcs each-tof which has its centre .at one of :the`corners .of the hexagon. The portion of theducts IA, H5 Whichliesladjacent the hexagonal collector I5 and .between side 'Il, of thelatterand the line c, for instance, consists of Aa plurality of.ccncentricarca the centre of which is at ed. The ,portionlof said ducts'flying l-between side slfl" `of .thezcollecton .the .line c and theline c .consists of a .plurality of concentric circular arcswjhosecornmon-.centre lies atc'. In this construction with.a-.preselected uniform fduct width .a1 :the passage vwidth .b- :will

beconstant throughout the vler-agtnof :the-ducts."

Figure :5shoW-s .za similar constructionstoithat fof, :Figure l in .sofar as Athe ducts Ill, IB .are lof liinvolute form. linstead pcf, theinvolute being generated from .a circular collector as .is :the-case .inEigure 1, :the base (for the involute .is"an elliptical collector t5.Since A.the ducts are of .involute form the vselection of a uniform ductEwidth a will result in the passage vw'idtlr'b also beingvunitorm;throughout the length ofthe'ducts.

Figure .6 .shows :a construction VinV whichY theI` .i-ing of ancircle Veabout .afcircular collector I5 so that, for instance, point .ff on :thecircle describes path -g .which lis 'the :path :followed `by the yductsA A4, fl.. In thislconstruction the ducts lil, :t6 vare ofeepicycloidalform .and are suchthat 'byprovidinga constantlxluc't .width wlthepassage wid-th .bfwill tbe approximately constant throughout the lengthof the :ducts provided '.thatrthe diameter'.

ofnthe rolling circle great/compared with that* of the collector titi.Ashe/tween rlucts o Atheforrn shown in Eig-urea' and ducts yoi" involuteform :it -is found that 'fior .the same drum ande-entrai collectordiameters the .epicycloidal duct -is fthe Alonger of atheitwo. Thelength of an 'epicycloid'4 lAby erolling Aof Va circle .arouridthecentral collector 5115 circle being -of larger-diameter:thanv-thec'oll'ector and lying outside and lpoint contact iwithsaidcollector. curve thus genteratedisazhypo'cycloid and hassimilarproperties to the epi-cycilcid, namely that by selecting fauniform 'duct fwidthc the passage "wld-th ll) vwill fbeapproximatelyfconstant throughout the vller'rg-th `-ofith'elidr-rots. Y

vVarious moaications vto the construction of :heat-exchanger shownFigures 'l to 6 inclusive Smay Joe lmarl-e Whilst vretaining y theessential fea'- A-ture's Iofv the invention `iin :which uniformity of.wid-th Vis provided for 'the ducts vand passages. vForinstance asfshoffn-'inF-i'g-ure the collector 4% may have -an inner bounding Wall2l -so that fsall central y--cl.'1smiloer iis of rannular Yfior-rn. Thismenstruation is particularly suitable Whereit '-is t-vfclaesired to atransmissioncr other shaft 22 oentrfallyfthroughetheheat-eXchanger.VGlhewvall of the col-lector as inrrglueu may'fbeicyundrreal 11, 2,4-and5 the coldairpassing inwardlyalong -ducts 14 is discharged intoa'common chamber.

fcertain 4'cases it may 'beound preferable 'to ensure that'the-cold airnfrom `one of the ,cham- Jbers lf3 passes 4'toits associated :'hot--airChamber 1% without mixing in' collector 15. with thegases *from the.other'jco'ld-jair chambers To this end "the central chamber rnay 'be'provided Ywith a spider `l24 :CFigure 6) whose radial arms extendoutwardly to form@ plurality of sealed compart- 'ments "25 veach .ofvvhichlis associated with la cold-air chamber V,and ahot-ar chamber.

, When the ducts t4, IE5 shown in ,any .of .the constructions of Figuresn1Y ,to 6 'are made from parallel Wall tubes it 'is arranged that banks.of such.tubesjextend along the "length of the heatexchanger trunk.. thetubescf .the .various banks beingaligned sof asQto providestraight-through passages 1S for the exhaust gases.

uan alternative to the ,provision lof tubular ducts 11% 1.1i said ductsmaybe ormedin pairs ofy plates Whichextend lengthwise vthrough the.trunk II, and viewed .ndwis'e (that in Athe direction or `flow oftheexhaustrgases) arecum/.ed to Oncol l,the shanesilescribedwlthreferenceto Figures 1 gto, Each plate'iof a pair is ,crimped at'intera/'als A along vTits length so as 'to .abut the other plate .andis Alimited thereto, ,the crimps .extending from the' 'edgecf the .plate.which vis -secured 'to the ,Wall Il .of .the collector .l5 to the edgewhich'is .secured to the .wall .l 2 .of 7the .trunk "I I, vfl'hereoistherebyprovideda .unit Whichcoln- .prises Ya plurality -of .ductsside-byside open .at one end to the nteriorcf'the collector .I Eand atthe other .end to .a coldfair chamber I3 or a lnotairchamber I8. `.Sinceeach unit .or .pairQo Aplates extends.along'fthelengthcf the trunk Jl..it provides a row of ductsivhohare placedone -behind ,the a,other.viewed .endwise of the trunk.

` jIt Wllbeobv'ious that with'this arrangement also,

.the units wllllprvide straight-.through passages 'I9 -for .the .exhaustgases.l these ypassages Jo'eing jorlm'edbetween thelad-jacent plateunits. The preferred :embodiment of the present .n- `ventfion isshown'in Eigures ,7, .8 ,and ,.9 of the accompanying ,drawings I f Referring'toFigure 8:i't Willjbe .notedthat .the ends of .the 'heaterareclosed'by v.Dlates..".l be- Ltween .whjch Va,plurality-of parallel tubes21 extend. 'lhelexhaust gaseslfrom the .turbine pass 'through said'tubesto the discharge nozzle. The end lplates .246.'are for-.med around4.their circumference :witha pluraltyof .spaced Vears 3| each ofwhichfis adapted `t'osupport a hood.-33 that .eX-tends :trom an ear,associated-with ...one plate to-a correspondingyear associated with theother end plate. fhood :assemblage constitutes ,fonesof the:hotecr'ifcold-a-ir chambers vil!! sand #|13 refe-fred@ to above. airlrom'zthecompressor (and to the turbine) isrcafnred by l'ips met shown)which are attached to nanges i The air chambers lI1! and then passesinwardly between the tubes 21 to a collector I5 disposed at the middleof the heat-exchanger. The partially heated air then flows outwardlyfrom the collector between another series of the tubes 21 to the hot-airchamber I8 which is in communication with the turbine.

As shown in Figure 7 thetubers 21 are arranged side by side in apluralityV of rows generally indicated at 36. Each row is formed bylocating the.Y

centres of a number of said tubes upon an involute curve as viewed inthe direction of ilow of the exhaust gases through the tubes. Theplurality of tubes 21 which constitutes one of the rows 3-6 isequivalent to the passage I9 referred to in the descriptions of Figures1 to 6 whilst the spaces between the rows (along which Vis conveyed thecold air from the chambers I3 and the partially heated air movingtowards chambers I8) are equivalent to the ducts I4 and I6. It will beappreciated from Figure '7 that the passage width b being predeterminedis uniform throughout the length of the rows. With this uniform passagewidth and with the tubes 21 disposed in involute rows the width a of theducts I4, I6 is also uniform throughout their length.

The tubes 21 are oval in cross-section the shorter distance betweenopposite walls being equal to the passage width b. In order to pro- Videadequate support for the multiplicity of tubes the end plates 26 are,formed with involute slots 28 and a flange 29 bounding said slots. Theends of the tubes 26 are received by the slots 28 and flanges 29. Theabutting faces of adjacent tubes in the rows are maintained in contactby a packing piece 30 which is inserted if required at the outer end ofthe slots 28. So that the tubes 21 lmay form a gas tight connection withthe involute slots 28 by which they are carried the ends-of the tubesare upset into a trapezoidal cross-section (see Figure 9). As aconsequence 'the abutting faces of adjacent tubes 21 are broughtintointimate contact with each other whilst the faces of the tubes whichengages the sides of the involute slots 28 make good contact therewith.When the trapezoidal ends ofthe tubes 21 are brazed or welded into theslots 28 a gas-tight vjoint is obtained. For convenience there has beenshown in Figure 7 an involute slot 28 which is devoid of the pipes 21,and an involute slot 28 showing the disposition of the trapezoidal endsof the tubes 21 therein.

The plates 26 (as shown in Figure 8) extend completely across the endsof the heat-exchanger so that the exhaust gas is constrained to flowalong the tubes 21 being prevented by said plates from mixing withtheair passing along either the ducts I4, I6 or with the air in thecollector I5.

In the construction shown in Figures 7 and 8 the tubes 21 may -bereplaced by pairs of plates .bent to an involute shape as described invone of the constructions above, the plate being crimped and united withthe crimps extending parallel with the flow of the exhaust gases throughthe heat-exchanger.

Although in each of the embodiments described above the collector I iscoincident with 'the base from which the curve for the ducts isgenerated this need not be so. The collector may be of greater or lessdiameter than said base. Moreover, the regular geometrical figureforming the base for the generation of said curve may in `certain casesbe different from the geometrical Aoutline of the collector.

I claim:V 4LA heat-exchanger comprising a plurality of spaced ducts forone fluid extending from the periphery of said exchanger toward the axisthereof and forming passages between said ducts through which anotherfluid flows axially of said exchanger, the walls separating said ductsand passages being so curved in planes at right angles to said axis thatsaid ducts and passages are of substantially uniform width when measuredin planes at right angles to said axis, a plurality of inlet headersdisposed around said heat-exchanger and communicating with the outer endof some of said ducts, and a plurality of outlet headers disposed aroundsaid heat-exchanger and intercalated with said inlet headers, saidoutlet headers communicating with the outer ends ofthe remaining ductsand said last named ducts communicating with the inner ends of the ductsin communication with said inlet headers.

2. A heat-exchanger comprising a plurality `of spaced ducts for onefluid extending from the periphery of said exchanger toward the axisthereof and forming passages between said ducts through which anotheruid flows axially of said exchanger, the walls separating said ducts andpassages being so curved in planes at right angles to said axis thatsaid ducts and passages are of substantially uniform width when measuredin planes at right angles to said axis, the curvature of said wallsconforming to the locus of a point on a line that rolls without slidingaround a regular geometrical gure in a plane at right angles to theaxis, a plurality of inlet headers disposed around said heat-exchangerand communicating with the outer end of some of said ducts, and aplurality of outlet headers disposed around said heat-exchanger andintercalated with said inlet headers, said outlet headers communicatingwith the outer ends of the remaining ducts and said last named ductscommunicating with the inner ends of the ducts in comlmunication withsaid inlet headers.

3. A heat-exchanger comprising a plurality of spaced ducts for one fluidextending from the periphery of said exchanger toward the axis thereofand forming passages between said ducts through which another fluid owsaxially of said exchanger, the walls separating said ducts and passagesbeing so curved in planes at right angles to said axis that said ductsand passages are of substantially uniform width when measured in planesat right angles to said axis, said walls having an involute curvature, aplurality of inlet headers disposed around said heat-exchanger 'andcommunicating with the outer end of some of said ducts, and a pluralityof outlet headers `disposed around said heat-exchanger and intercalatedwith said inlet headers, said outlet headers communicating with theouter ends of the remaining ducts and said last named ductscommunicating with the inner ends of the ducts in communication withsaid inlet headers.

4. A heat-exchanger comprising a plurality of spaced ducts for one fluidextending from the periphery of said exchanger toward the axis thereofand forming passages between said ducts through which another fluidflows axially of said exchanger, the walls separating said ducts-andpassages being so curved in planes at right angles to said axis thatsaid ducts and passages are of Substantially uniform width when measuredl in planes at right angles to said axis, the curvature of said wallsconforming to the locus of a astanti disposed around'sad heat-'exchangerand cornniunioaing with the outer end 'of some olf said ducts', and aplurality' of outlet headers disposed around said heatfexchanger andintercalated with said inlet headers, said outlet headers communicatingwith the outer ends of the remain- Y ing ducts and-said'last namedductscommunieating with the inner ends of the d cts in `cemmunication Withsaid inlet headers. s

5. A heat-exchanger comprising a plurality of spaced ducts forone fluidextending from the periphery of said exchanger toward thef'axis thereofand forming passages between said ducts through which another rluidllowsaxially ofA said exchanger,y the walls separating .said ducts andpassages being .so curved in planes at right angles to said axis thatsaid ducts and passages are of substantially uniformi width whenmeasured irl-planes at right angles to ysaid axis, the curvature `ofsaid walls conforming too'ircular arcs that approximate to the locus ofa point on aline that rolls without sliding around a regular geometricalfigure in a plane at right angles to said axis, a plurality of inletheaders disposed around said heat-exchanger and communicating with theouter end of some of said ducts, and a plurality of outlet headersdisposed around said heat-exchanger and intercalated with said inletheaders, said outlet headers communicating with the outer ends of theremaining ducts and said last named ducts communicating with the innerends of the ducts in communication with said inlet headers.

6; A heat-exchanger comprising a plurality of spaced ducts for one iluidextending from the periphery of said exchanger toward the axis thereofand forming passages between said ducts through which another fluid Howsaxially of said exchanger, the Walls separating said ducts and passagesbeing so curved in planes at right angles to said axis that said ductsand passages are of substantially uniform Width when measured in planesat right angles to said axis, the curvature of said walls conforming tothe locus of a point on a circle that rolls Without sliding around aregular geometrical ligure in a plane at right angles to said axis, aplurality of inlet headers disposed around said heat-exchanger andcommunicating with the outer end of some of said ducts, and a pluralityof outlet headers disposed around said heat-exchanger and intercalatedwith said inlet headers, said outlet headers communicating with theouter ends of the remaining ducts and said last named ductscommunicating with the inner ends of the ducts in communication withsaid inlet headers.

7. A heat-exchanger comprising a plurality of spaced ducts for one fluidextending from the periphery of said exchanger toward the axis thereofand forming passages between said ducts through which another fluidflows axially of said exchanger, the Walls separating said ducts andpassages being so curved in planes at right angles to said axis thatsaid ducts and passages are of substantially uniform width when measuredin planes at right angles to said axis, the passages between said ductsbeing composed of axially extending tubes disposed side by side toconstitute chains, a plurality of inlet headers disposed around saidheat-exchanger and communicating with the outer end of some of saidducts, and a plurality of outlet headers disposed around saidheat-exchanger and intercalated with said inlet headers, said outletheaders communicating with the outer ends of the remaining ducts andsaid l0 last named uuctsccmmunicating with the inner ends of the ductsin communication with said inlet headersl, U f

8.A Az heat-exchanger 'comprising a plurality of spaced 'ducts "for 'onefluid extending from the periphery -of ysaid exchanger'toward Vthe axisthereof and' forming passages between saidV ducts through whichaho'theriiuidflows axially of said exchanger, the lwalls separatingsaidducts and passages being so curved in planes at right angles4 to saidkaxis 'that saidjductsahd passages are of substantialiy uniform widthlwhen `n ieasured in planes atright angles to said/axis, the passagesbetween said ducts'being composed of axially 'extending tubes disposedsid-e by side to constitute chains, a'pluralitypf, inlet vheadersdisposed around said heat-exchanger and communicating with the louterendlof some of said ducts, a plurality of 'outlet headers disposedaround said heat-exchanger and intercaia'ted with said inlet headers,said outlet headers communicating'with the outer ends of the remainingducts and said last named ducts communicating with the inner ends of theducts in communication with said inlet headers, and plates provided withcurved slots in which the ends of said tubes are disposed.

9. A heat-exchanger comprising a plurality of spaced ducts for one uidextending from the periphery of said exchanger toward the axis thereofand forming passages between said ducts through which another fluidflows axially of said exchanger, the walls separating said ducts andpassages being so curved in planes at right angles to said axis thatsaid ducts and passages are of substantially uniform Width when measuredin planes at right angles to said axis, the passages between said ductsbeing composed of axially extending tubes disposed side by side toconstitute chains, a plurality of inlet headers disposed around saidheat-exchanger and communicating with the outer end of some of saidducts, a plurality of outlet headers disposed around said heat-exchangerand intercalated With said inlet headers, said outlet headerscommunicating with the outer ends of the remaining ducts and said lastnamed ducts communicating with the inner ends of the ducts incommunication with said inlet headers, and plates provided with curvedslots in which the ends of said tubes are disposed With the walls of theadjacent tubes in contact.

10. A heat-exchanger comprising a plurality of spaced ducts for onefluid extending from the periphery of said exchanger toward the axisthereof and forming passages between said ducts through which anotherfluid flows axially of said exchanger, the Walls separating said ductsand passages being so curved in planes at right angles to said axis thatsaid ducts and passages are of substantially uniform width When measuredinV planes at right angles to said axis, said walls being crimpedtogether in pairs to form tubes constituting axially extending passagesand disposed in a side by side chain-like arrangement, a plurality ofinlet headers disposed around said heatexchanger and communicating Withthe outer end of some of said ducts, and a plurality of outlet headersdisposed around said heat-exchanger and intercalated with said inletheaders, said outlet headers communicating with the outer ends of theremaining ducts and said last named ducts communicating with the innerends of the ducts in communication with said inlet headers.

1l. A heat-exchanger comprising a plurality of spaced ducts for one uidextending `from the periphery of said exchanger toward the axis thereofand forming passages between said ducts through which another fluidflows axially of said exchanger,. the walls separating said ducts andpassages being so curved in planes at right angles to said axis thatsaid ducts and passages are of substantially uniform width when measuredin planes at right angles to said axis, a plurality of inlet headersdisposed around said heat-exchanger and communicating with the outer endof some of said ducts, a plurality of outlet headers disposed aroundsaid heat-exchanger and intercalated with said Vinlet headers, saidoutlet headers communicating with the outer ends of the remaining ductsand said last named ducts communicating with the inner ends of the ductsin communication with said inlet headers, and an inner axially extendingchamber consituting a means of communication between the ductsrespectively communicating with the inlet and the outlet headers.

12 12. A heat-exchanger asv defined in claim 8 wherein at least the endsof the tubes are of trapezoidal cross section to completely ll theslots. Y

ALEC GEORGE HENSTRIDGE.

REFERENCES CITED The following references are of le of this patent:

UNITED STATES PATENTS record in the

